A lealdade à varinha depende dos materiais da varinha. (Jogando algumas citações de Rowling no final do post).
Nós não sabemos do que a varinha de Snape é feita, mas pode ou não ter mudado a lealdade, embora possamos assumir em algum nível baseado nas citações de Rowling que ela levou pelo menos uma pequena lealdade a cada um dos os 'desarmadores' (dando um salto aqui com base na idéia de que a personalidade de Snape não o teria emprestado a um par de unicórnio ou um núcleo de pena de Fênix).
Independentemente disso, Harry, Ron e / ou Hermione não conseguiram mantê-lo ou usá-lo (por isso, não podemos dizer o quanto teria funcionado para eles) e, embora a lealdade absoluta possa ter mudado, ainda teria uma aliança com Snape, portanto ainda funcionaria para ele.
Citação da entrevista com JK Rowling encontrou AQUI sobre a lealdade à varinha:
MA: But wand lore. Can you go into-- in a more detailed fashion, the way that the wands change hands and how different the Elder Wand is because fans are confused.
JKR: I am going to put up another update on my website about this, and I have one half-written. Essentially, I see wands as being quasi-sentient, you know? I think they awaken to a kind of-- They're not exactly animate but they're close to it. As close to it as you can get in an object because they carry so much magic. So that's really the key point about a wand. Now, the reactions will vary from wand to wand. The Elder Wand is simply the most dispassionate and ruthless of wands in that it will only take into consideration strength. So one would expect a certain amount of loyalty from one's wand. So even if you were disarmed while carrying it, even if you lost a fight while carrying it, it has developed an affinity with you that it will not give up easily. If, however, a wand is won, properly won in an adult duel, then a wand may switch allegiance, and it will certainly work better even if it hasn't fully switched allegiance for the person who won it. So that of course is what happens when Harry takes Draco's wand from him, and that's what happens when-- But you know what I mean. Oh, yeah, Ron. The blackthorn wand from the snatcher. So that would be sort of rough and ready, common, or garden, a wand favoring the person who had the skill to take it. It would favor them. However, the Elder Wand knows no loyalty except to strength. So it's completely unsentimental. It will only go where the power is. So if you win, then you've won the wand. So you don't need to kill with it. But, as is pointed out in the books, not least by Dumbledore because it is a wand of such immense power, almost inevitably, it attracts wizards who are prepared to kill and who will kill. And also it attracts wizards like Voldemort who confuse being prepared to murder with strength.
Algumas citações de Rowling sobre certos núcleos de varinhas encontraram AQUI
The Elder Wand (Threstal hair core) is extremely fickle and responds readily to power, with zero loyalty to its previous owner. The allegiance of this wand is won very easily using brute force, but never peacefully (For instance, Snape killing Dumbledore with Dumbledore's consent wouldn't make Snape the master of the Wand.)
Unicorn hair wands are very loyal; in fact they are the most faithful and don't care much about skill or power. They generally will always be attached to its original owner, regardless of current allegiance.
Phoenix feather wands are also very loyal because they are very picky when choosing their first owner. It can be quite difficult to win their allegiance because of this.
Dragon heartstrings wands are more similar to the Elder Wand; they appreciate power, so it is easier to win their allegiance from their previous owner.